You would only expect millionaires to have very high GPAs if being a millionaire didn't require anything else. Slightly more accurately, you would only expect

You would only expect millionaires to have very high GPAs if being a millionaire didn't require anything else. Slightly more accurately, you would only expect millionaires to have very high GPAs if being a millionaire involves no variables that are independent of GPA. For example, let's say that SAT scores and GPA are highly correlated. If the government runs a program whereby they give $1M to everyone who gets a perfect SAT score after they graduate from college, then the mean GPA of millionaires would skew much higher despite the dependent variable being SAT scores rather than GPA.